Step 4: Transistors
There are three leads on a transistor, labeled "B," "E," and "C." These stand for "Base," "Emitter," and "Collector."
If there is no current flowing to the base, the transistor won't let the emitter and collector receive any current.
There are several types of transistors, two of them are NPN and PNP. "N" stands for negative, and "P" stands for positive. NPN means that the outer two leads are negative and the inner lead is positive. PNP means the exact opposite.